Three main projects are proposed, all using micropuncture methods to study renal function. 1. The role of parathyroid hormone (PTH) in acid-base balance will be studied. PTH, cyclic-AMP, or dibutyryl cyclic-AMP will be infused in parathyroid-ectomized rats. Bicarbonate reabsorption by the proximal tubules will be measured before and after the infusion, to determine any inhibition of HCO3 reabsorption that might occur. Similar experiments will be carried in 3/4 nephrectomized rats with secondary hyperparatyhroidism, to simulate conditions in patients with chronic renal disease. 2. Peritubular colloid oncotic and hydrostatic pressure will be measured in rats with 2 kinds of renal disease, a sodium-retaining nephrotic syndrome and a sodium-losing pyelonephritis. Sodium reabsorption by the proximal and distal tubules, as well as over-all sodium balance will be correlated with the peritubular Starling forces. The objective of this study is to determine whether changes in peritubular physical forces can account for abnormal handling of sodium and water by the diseased kidney. 3. The intraluminal chemical constituents which effect fluid reabsorption by the proximal renal tubule will be studied by microperfusion techniques. A systematic survey of the role of electrolytes, amino acids, and glucose in determining the rate of fluid absorption will be made. The purpose of this study is to define the basic intraluminal chemical requirements for optium sodium and water transfer.